"CRON: There are 1 expiring relationships" What does it mean?

I'm using your membership 1 plugin(
But,When I update from, All of my users saw "protected contents" message.
Maybe, Update program has something wrong.
So,I used Debug-mode.

This is the debug message.
[19-Oct-2015 17:12:30] loading level premium *<- this is my premium membership level I created.
[19-Oct-2015 17:12:30] Standard levels are loaded for current member.
[19-Oct-2015 17:12:30] Current member can not view current page
[19-Oct-2015 17:12:31] CRON: There are 1 expiring relationships

Do you have any idea?

I took a guess that my some membership DB-tables now have wrong data.
Maybe, version) don't use those data,so works fine.
But is using them. (ex wp_m_member_payments),
So All of my member are force to move visitor-level in spite of their real level(premium).